The Regenerative Burners

How is The Application On the Melting Furnaces: The regenerative burner consists of  a compact regenerator strictly  connected to a burner. A complete R.C.B. unit is constituted of  regenerators, burners, a reversal valve  and the connected reversal control systems. At the beginning, one burner fires using  cold air fed to the base of the regenerator,  meanwhile the flue gas produced by it,  cross the other burner and  the regenerator coupled to it, preheating  the ceramic lining and drawing off  in the atmosphere  (the second burner is acting,  practically, as an exhaust part). When the regenerator is sufficiently hot,  the reversal system starts, the cold air flows  inside the just heated regenerator  and preheats, meanwhile the first burner  regenerator will be heated by the flue gas  produced by the reversal burner. The direct connection of the burner  to its own regenerator and the alternate  functioning of the burners allow  to eliminate valves, working at  the flue gas temperature, according  to all the related problems. The reversal valve is requiring, to function,  compressed air and electrical energy for  the reversion programming logic,  based into a combination  of time and/or flue gas temperature. This reversal system is completely independent  from the other furnace controls, with the exception of the flame protection,  to which the burner starting sequence  has to be connected. The proportion between air and gas is controlled  by means of a differential input, from a  gauged hole diaphragm, positioned along  the combustion air line and from  a frequency multiplier governor, to send a signal,  based on the delivery, to a air/gas ratio regulator. The combustion air flow of the flue gas is controlled  by means of two tandem valves, set by  the processus temperature controller. The flue gas setting is obtained by means  of a motorized valve, controlled by  the furnace pressure, installed at the exit  of the suction fan. This fan is protected against eventual overheating. PECULIARITIES Two R.C.B. burners/regenerators,  together with their reversal system,  need only an electrical connection  for the logic and compressed air  to position the reversal valve, in addition  to the normal gas and combustion  air feeding lines and to the usual flames  and flue gas exit control and safety devices. The combustion air and flue gas deliveries  are tandem controlled by  the processes temperature controller. The flue gas fan (usually a conventional cold air fan)  is protected from an eventual overheating  by a thermostat that, if necessary, releases  the alarm and switches off the burner.  The exhaust fan protection valve allows  to the ambient temperature air to enter  in the fan same. The flue gas level can be set by a furnace  pressure control, that drives a valve, installed  at the flue gas suction fan exit. The flue gas flow switching  (from a burner to the other) is realized  by an electrovalve. The control of air/gas ratio is obtained  by means of a subsidiary cold air system. An air/gas ratio regulator, that functions proportionally  to the differential signal, taken by a gauged  hole diaphgram is recommended  for its simplicity and reliability. The ignition of the R.C.B. is realized by a pilot burner,  lighted by a candle. The burner is already functioning under U.V. rays  flame control, at gas low delivery,  corresponding to 2-5% of the max. nominal delivery. This practice eliminates the relighting  of the burner at each reversal. The cold air setting and control valves,  installed on the flue gas line, are conventional,  if a sufficient clearance among  the mobile parts is foreseen. ELECTRICAL CONTROL SYSTEM The electrical control system is supplied  with a special pre-wired control panel. The fans starters, the burners managing system,  the P.L.C. control system and the relays  are fit in this panel. The burners management is actuated  by flame control (one for each burner),  utilizing ultraviolet rays flame detectors. Manually, the temperature control system  is supplied as a “three unites” controller (P.I.D.),  positioning the motorized butterfly valves  on the combustion air and flue gas line. Obviously it might be supplied according  to the Customer’s requests or to the processes. The reversal system controls  the combustion functioning period of the burners.  This system is operating continuously,  when the control panel is inserted. The basic parameter to be measured, to determine  the reversal point, is the flue gas temperature  at the regenerative exit. The flue gas temperature allows to balance  the efficacy in the two directions, as it represents  the best quantity released to the regenerator. Maximum time limits are foreseen,  to assure and maintain the pre-heating and  to avoid a too high temperature of the flue gas,  during the functioning. As above specified, the control system utilizes  a combination of relays and electronic logic. The relays are utilized to control the faults and  to check the position of the valves. GENERAL CHARACTERISTICS Possibility to operate up to temperature of 1.200°C. The burner and the regenerator  are manufactured with ceramic material and  refractory lining in the hot part, to resist  to a temperature of 1.200°C of the flue gas  and to a temperature of about 1.100°C of  the preheated air. High efficiency The regenerative burner (R.C.B)  has a higher efficiency,  compared with the traditional one. In fact regenerators and recuperators  that supply preheated air only to the processes  from which the smoke is drawn, are limited  for what is regarding to the quantity of heat  to be extracted from the flue gas. The combustion air cannot be heated  to a temperature higher than the temperature of the processus.  Furthermore, the flue gas mass will be higher  than the combustion air,  with a specific heat higher than the combustion air. The calorific balance shows that the max. quantity of recoverable heat, at 1.024°C, is around 83%. The regenerative burner R.C.B. is in condition to recuperate from 85% to 90% of this value. High energy saving. By the high energy saving level, utilizing the R.C.B. burner, it is possible to save, at a processes temperature of 1.200°C, around 40%, compared with a cold air system, and 20% compared with a traditional heat recuperating system. Possibility to operate with polluted exhaust. The materials utilised for the manufacturing of the R.C.B. have been chosen for their properties to resist to the heat and to the chemical agents. The exhaust, typical of the industrial processes, contains sulphur, alkali and metallic oxides, that can contribute to a very fast wearing of the materials constituting the recuperator, because of hot corrosion and of deposits, causing a reduction of the results, due to incrustations and occlusions. The R.C.B. burner has demonstrated to be in condition to operate, installed at direct Combustion, in a melting furnace for sodium-calcium glass, where all the volatile substances of the melting processes cross the recuperator filling. The experience has demonstrated that the filling can be removed, cleaned and easily and fastly replaced, without switching off the flame. The burners maintenance requires only the cleaning of the ceramic balls every 15÷30 days depending on the furnace production. This operation could be done with the furnace in temperature and requires a stop of about 2 hours. The balls must be simply washed plunging them in a small temperer with normal water. 1. Ceramic regenerative burner 2. Reversal valve 3. Combustion air /flue gas limitation valve 4. Combustion air /flue gauged hole disk 5. Combustion air / flue control valve 6. Fan protection valve 7. Combustion air gauged hole disk 8. Combustion air pressure switch 9. Degassing pressure switch 10. Low flame pressure switch 11. Exhaust fan functional control pressure switch 12. Gas high pressure - pressure switch 13. Gas low pressure - pressure switch 14. Flue gas fan 15. Combustion air fan 16. Impulses regulator 17. Impulses multiplier 18. Pilot burner air valve 19. Cooling air valve 20. Pilot burner mixer 21. Pilot gas interception valve 22. Main gas interception valve 23. Main gas limiting valve 24. Safety block electro valve 25. Pilot gas block electro valve 26. Air/gas ratio regulator 27. Pilot gas regulator 28. Main gas regulator reducer 29. Gas intercepting valve 30. Furnace pressure control valve CERAMIC BODIES OF REGENERATING BURNER CLEANING PROCEDURE The only maintenance required by ceramic bed of the recuperator is the spleres cleaning. Maintenance intervals are strictly connected to the specific furnace use; they can be determined monitoring combustion performance. The main factor to indicate that a cleaning procedure must take place is the drop of pressure measured through the regenerating bed. The pressure difference (Δp) is the value calculated from the measure carried out on pressure test points 1 and 2, respectively downstream and stream the regenerator.